To begin it is disclosed that the bi-lateral slit assembly of Co-owned U.S. Pat. No. 5,661,589 is revisited as part of the presently disclosed invention. Further, the disclosed invention includes in some embodiments a multiple detector system as disclosed in Allowed application Ser. No. 09/531,877, (now U.S. Pat. No. 6,535,286), from which this Application Continues-in-Part via Co-Pending application Ser. No. 10/376,677, Filed Feb. 28, 2003.
Spectroscopic ellipsometry (SE) was developed in the early 1970's after single wavelength ellipsometry had gained widespread acceptance. The first (SE) systems provided limited Ultraviolet (UV) to near Infrared (IR) spectral range capability, and with the exception of a few research instruments, this remained the case until the 1990's. Many challenges faced development of (VUV) ellipsometer systems, including the fact that many optical element materials absorb in the (VUV) wavelength range. Vacuum Ultraviolet (VUV) ellipsometry was so named as it was initially carried out in vacuum, however, the terminology is today applied where purging gas such as nitrogen or argon is utilized in place of vacuum at wavelengths, typically with an energy less than about 10 ev. The reason (VUV) ellipsometry must be carried out in vacuum or purging gas is that (VUV) wavelengths, are absorbed by oxygen and water vapor.
In the mid-1980's a Spectroscopic ellipsometer was constructed at the BESSY Synchrotron in Berlin for application in the (VUV) wavelength range, (eg. 5–35 eV), and in the 1990's Spectroscopic ellipsometry was achieved in the Extreme Ultraviolet (EUV) range, (eg. greater than 35 eV), at KEK-PF. Application of ellipsometry in the (VUV) and (EUV) wavelength ranges remained restricted to said research facilities until in 1999 commercial (VUV) ellipsometer systems became available from companies such as the J.A. Woollam Co. Inc. At present there are approximately twenty-five (VUV) Systems in use worldwide. It is noted that commercial (VUV) instruments, which provided wavelengths down to 146 nm, were introduced in response to the need for bulk material properties at 156 nm, which is utilized in lithography as applied to semiconductor gate oxide production.
The practice of ellipsometry, polarimetry, spectrophotometry, reflectometry, scatterometry and the like, using Infrared (IR), (eg. 2–33 micron), and Ultraviolet (UV), (eg. 135–1700 nm), Electromagnetic Radiation Wavelengths, then is, as disclosed above, known. As mentioned, electromagnetic Radiation with wavelengths below about 190 nm is absorbed by atmospheric components such as Oxygen and Water Vapor. Thus, practice of Ellipsometry etc. using VUV Wavelengths is typically carried out in vacuum or an atmosphere which does not contain oxygen and/or water vapor or other absorbing components. The J.A. Woollam CO. VUV-VASE, (Registered Trademark), for instance, utilizes a Chamber which encompasses a substantially enclosed space which during use is purged by Nitrogen and/or Argon or functionally equivalent gas. (Note Nitrogen does not significantly absorb UV Range wavelengths above about 130 nm, and Argon is in some respects even a better choice as it has an even lower yet onset of UV Range wavelength absorption). Further, the source of the electromagnetic radiation in the J.A. Woollam CO. VUV-VASE is preferably a Deuterium Lamp or a Xenon Lamp present within a J.A. Woollam Co. monochromator system which produces wavelengths of 115–400 nm, (of which 135–190 nm is used), and up to about 2000 nm, respectively. Specific wavelengths are selected by said J.A. Woollam Co. Monochromator which comprises a specially designed Cherny-Turner Spectrometer.
It is beneficial to note that Spectroscopic Ellipsometry (SE) is practiced utilizing an ellipsometer system generally comprising:                a source system comprising:                    a source of electromagnetic radiation: and            a polarization state modifier system:                        a stage for supporting a sample system;        a plurality of polarization state detector systems, each of which comprises:                    a polarization state analyzer: and            a detector system;such that a beam of electromagnetic radiation is produced by said source of electromagnetic radiation and caused to pass through said polarization state modifier system, interact with a sample system placed on said stage for supporting a sample system, pass through a polarization state analyzer and enter a detector system in the pathway thereof. It is noted that the terminology “a source” can include multiple sources which serve to provide a beam of electromagnetic radiation in different wavelength ranges.                        
The standard J.A. Woollam CO. VUV-VASE Spectroscopic Ellipsometer system sequentially comprises, mounted inside substantially enclosed space within a Chamber:                a monochromator;        a beam polarizing means;        a polarization state modifying means as described in U.S. Pat. Nos. 5,956,145 and 5,757,494;        a beam alignment detector means such as a quad detector as mentioned in U.S. Pat. No. 5,872,630 in Col. 20, Lines 55–57;        a stage for supporting a sample system;        an analyzing means; and        data detector means;wherein said monochromator comprises;        a) source of electromagnetic radiation;        b) a first slit in a first slit providing means;        c) a first mirror;        d) a first stage comprising a plurality of gratings, each of which can be rotated into a functional position;        e) a second mirror;        f) a second slit in said second slit providing means;        g) a third mirror        h) a second stage comprising a plurality of gratings, each of which can be rotated into a functional position;        i) a fourth mirror;        j) order sorting filter means;        k) a pin hole;with a beam chopper being present after said source of electromagnetic radiation, (typically, but not necessarily, just prior to said pin hole).        
In use an electromagnetic beam from said source of the electromagnetic radiation is:                caused to pass through said first slit;        reflect from said first mirror;        interact with one of said plurality of gratings on said first stage which is rotated into a functional position;        reflect from said second mirror;        pass through said second slit;        reflect from said third mirror;        interact with one of said plurality of gratings on said second stage which is rotated into a functional position;        reflect from said fourth mirror; and        proceed through order sorting filtering means; with monochromator selected wavelengths being caused to exit through said pinhole.        
The beam is also chopped by beam chopping means placed somewhere after the source of electromagnetic radiation, (typically, but not necessarily, just before the pin hole providing means).
The gratings on said first and second stages are independently rotated into precise desired functional positions via stepper motors controlled by computer. This has proven to provide superior precision and repeatability than commercially available grating positioning systems, at least in part because the J.A. Wobllam Co. system does not control one grating supporting stage as a slave to the other, as is done in known competing systems. Again, in use, the stages which support the gratings are independently rotated to optimum orientations.
Further, it is disclosed that an electromagnetic radiation beam produced by said J.A. Woollam CO. Monochromator has been shown to provide a highly collimated beam, with typical defining parameters being a 5 mm diameter at the pinhole output of the Monochromator, with divergence to about 20 mm diameter at 20 Feet, (ie. 6000 mm). This represents a divergence angle of only about 0.00125 radians, (ie. 0.07 Degrees). The collimating optics comprises a spherical mirror in the optical path after the pinhole. Said spherical mirror collimates the beam and directs it to a flat folding mirror, and said flat folding miror directs the beam out of the monochromator.
While not new, it is noted that alignment of the Xenon Lamp follows a two step procedure. First it must be understood that the Xenon Lamps used have an Ellipsoidal Reflector associated therewith, which has a focal length and major and minor axes. The first step is to place the Xenon Lamp into the focal length position. This is followed by adjusting the major axis of the Ellipsoidal Reflector to be in line with the First Slit. The alignment procedure is typically monitored by maximizing intensity output from the Pin Hole.
It is also noted that the Deuterium and/or Xenon sources of electromagnetic radiation can be placed as indicated, but separate from the other components of the monochromator. For instance, in an ellipsometer system which sequentially comprises the Deuterium and/or Xenon sources in a Polarization State Generation System (PSG), a Sample System supporting Stage and a Polarization State Detector System (PSD), the components other than the Source of Electromagnetic Radiation can be placed in any functional location before or after the Sample System between the (PSG) and (PSD) or within one and/or the other.
Continuing, problems have been identified with application of the J.A. Woollam Co. monochromator system sold to date in that electrical wiring and motor driver electronic components have been included inside the substantially enclosed space in which specific wavelengths in electromagnetic beams are selected. As mentioned, outgassing from anything inside said substantially enclosed space can require very long periods of time, and substantial purging can be required where Vacuum-Ultraviolet (VUV) wavelengths are utilized. Further, diminished throughput of electromagnetic radiation with time has been traced to be, at least in part, caused by deposition and polymerization of polymers present in wire coatings on optical surfaces such as the surfaces of the mirrors and gratings inside the substantially enclosed space. It is also identified that electrical connections to components, such as the means for providing the first and second slits and rotation effecting means for the first and second grating stages, and the Lamp selecting mirror have, to date, been hard wired inside the enclosing means, thereby making replacement tedious. Further, the position of electromagnetic radiation source means present inside said substantially enclosed space must be adjusted to provide a beam which follows an intended locus. To date, position adjustments have required opening the enclosing means, thereby requiring additional purging where UV wavelengths are utilized.
Known patents include U.S. Pat. No. 5,303,035 to Ludcke et al., which describes a precision micropositioner that allows up to six degrees of motion freedom which are adjustable from controls located in a single plane. The mechanism involves forcing balls between support and ramped elements. It is noted that the range of adjustment is limited by the slope and length of the ramped elements. Specifically the present invention enables a greater range of adjustment. Other patents which describe the use of balls to transmit motion include No. 6,042,298 to Mastrogiannis et al. which describes the use of two sequences of balls oriented in manner so that forcing a wedge shape between the first ball in each sequence causes coupling of a joint between two sections in a frame. U.S. Pat. No. 4,656,780 to Miyauchi et al. describes an apparatus for reciprocally moving an object involving a string of interconnected balls. U.S. Pat. No. 4,062,251 to Parsons describes a sequence of interconnected balls in a ball cage, for the purpose of transmiting motion. U.S. Pat. No. 3,204,480 to Bradbury describes a motion transmitting means, again using a sequence of interconnected balls. U.S. Pat. No. 1,807,914 to Hopkins describes a lifting jack which incorporates use of a sequence of balls to transmit motion.
U.S. Pat. No. 6,414,302 B1 to Freeouf is identified as it describes use of VUV wavelengths which range up through 10 eV in systems which are used to investigate properties of solids.
Known patents pertaining to Multiple Detector Systems include a patent to Briggs, U.S. Pat. No. 3,405,270 describing a system containing slots which allow positioning of a source and detector relative to one another. A patent to Rayton et al., U.S. Pat. No. 1,773,436 describes a polarization photometer system with a bracket arm rotatable secured to a post, which is used to support a table and test specimen. U.S. Pat. No. 4,242,581 to Crow, describes a system of four laser energy detectors arranged to allow simultaneous energy monitoring, which system can be easily positioned with respect to a laser beam source aperture. U.S. Pat. No. 3,630,621 to Liskowitz provides a system for measurement of visibility through a fluid using polarized light wherein a source and a detector which are easily positioned with respect to one another. Other patents identified, but not felt to be particularly relevant are U.S. Pat. No. 4,938,602 to May et al., and U.S. Pat. No. 5,494,829 to Sandstrom et al. Patents identified by the Examiner in prosecution of the patent application Ser. No. 09/531,877, filed Mar. 21, 2000 include patent to Green et al. U.S. Pat. No. 5,956,145, patent to Johs et al. U.S. Pat. No. 6,353,477, patent to Rosencwaid et al. U.S. Pat. No. 6,278,519, patent to Herzinger et al. U.S. Pat. No. 6,084,675, previously identified patent to Johs et al. U.S. Pat. No. 5,872,630, patent to Drevillion et al., U.S. Pat. No. 5,557,671 and patent to Spanier et al., U.S. Pat. No. 5,166,752.
The disclosed invention provides improvements to the existing J.A. Woollam Co. monochromator system which are aimed at overcoming the identified problems.